1) Field of the Invention
The invention relates to a metal fuel tank with two tank shells which are welded together, an electrically driven fuel supply unit inside the tank, and also with lead-in ducts for at least one metal fuel line and for a connection device for supplying electricity to the fuel supply unit.
2) Description of the Related Art
Usually, the fuel supply unit is inserted into the completed fuel tank (top and bottom tank shells previously welded together) and the tank fuel supply is fastened to the tank by means of screw connections such as crown nuts and similar, or by screwing in the fuel supply unit as one would a bayonet. Rubber seals serve as sealing elements.
A specially designed device for sealing a fuel supply unit in a fuel tank is known from EP-A 0 921 299. Here, the fuel supply unit is inserted into a pod as a compact unit within housing. The pod has a cover through which at least one inlet nozzle and one electrical connection for the supply unit are fed through while the pod can be inserted into the fuel tank together with the whole unit by means of a tank adapter cap which is fastened to a tank flange. In this case, a rubber seal is provided which functions as an elastic bellows and sits in-between the pod cover and the tank flange.
State-of-the-art technology offers solutions which are all related in that they have large-volume rubber seals as sealing elements through which the fuel""s hydrocarbons can diffuse, since these substances are rubber-permeable. Recently in some countries, legal regulations have been planned regarding the requirements on the density of fuel tanks, especially regarding the diffusion of hydrocarbons to the outside. These regulations are much more severe than the ones applicable until now. The known solutions, especially the ones described above, can no longer fulfill these regulations or requirements.
Thus, the invention is based on the task of creating a fuel tank of the above type in such a way as to permit either no emission of hydrocarbons from the tank into the outside world or an emission reduced to an irrelevant minimum.
The invention solves this task by mounting the fuel supply unit from inside before the tank shells are welded together, and by having the lead-in ducts running through at respectively separated points through the tank shells and which are created using gas-tight means of connection.
The invention presented herein no longer requires a fuel opening in the tank for inserting the fuel supply unit, this opening being critical with regards to a gas-tight sealing. According to the invention, the fuel supply unit is already attached inside the tank while the tank is still two separate tank shells. The lead-in ducts for the fuel lines and for the connection device of the electric supply is also created locally and using gas-tight connection methods before welding the tank parts. Thus, the finished tank can be so tight as to no longer allow minimal leakage or no leakage of any hydrocarbon emissions outward.
The fuel supply unit can be mounted in an especially easy and useful manner by providing fastening elements which are placed on the inner side of the tank, more especially welded to it, onto which the fuel supply unit can be mounted.
Concerning gas-tight connecting methods, it is especially useful to weld or solder one metal part or component of the fuel line and/or of the connecting device to the tank. Welded or soldered seams are practically gas-tight.
The lead-in ducts can be created in an especially easy way by feeding the metal parts or components through a bore (or similar) in the tank and by welding or soldering them in the area of a peripheral flange which surrounds the bore.
For practical purposes, the metal part or component maybe the fuel line itself or a coupling nipple which is connected to it, especially by welding.
The connection to the fuel supply unit in the inside of the tank is also extremely simple. Here, the internal fuel line, which is more particularly a flexible hose, connects the fuel supply unit to the end area of the fuel line leading into the inside of the tank.
Also in the area of the connecting device""s lead-in ducts, a mainly gas-tight sealing should be ensured. For this, the metal part or component of the connecting device is intended to be a metal sleeve.
The feeding of the electrically conductive parts or elements through the connecting device is also important. In order to guarantee the best gas-tight sealing possible, the connecting device has a plastic part which sits inside of a metal sleeve and is sealed off from the encased conductive elements by at least one rubber seal.
This is also the only place(s) where at least one rubber seal can be used and it may have rather small dimensions. The mainly gas-tight seal is supported if the rubber seal is an O-ring seal which sits in a surrounding groove of the plastic part.
The source material of the rubber seal also plays a certain role. Preferable are seals based on fluorine elastomers, e.g. on FCM or fluorine silicone rubber, which are especially gas-tight.